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What is Disk Reliability?

Disk reliabilityrefers to an important property of any kind of database system. Reliable operation is very important for a system. One aspect of such a reliable operation is that all data captured in a committed transaction has to be stored in a nonvolatile area. An assessment help says that this very is safe in terms of power loss, operating system failure, and hardware failure. This kind of requirement can be met with successfully writing the data to the computer's permanent storage. In case when a computer is fatally damaged and the disk drives continue to exist. Such requirement can be moved to another computer with similar hardware. In this transaction process all committed will remain intact.

More About Disk Reliability:

Disk reliabilityforces data to disk platters in periodical manner. It might seem just like a simple operation but unfortunately it is not. Such disk drives are slower in comparison with main memory and CPUs. There are several layers of caching that exists between the main memory of the computer and disk platters. Initially, the buffer cache of the operating system can be requested disk blocks combining disk writes. All kinds of operating systems give applications in a method that force to write from the buffer cache to disk. This is possible to have a cache in the disk drive controller. It is commonly on RAID controller cards. They are write-back that means data to be sent to the drive at some later time. They can be some kind of reliability hazard as the disk controller cache memory is unstable. It loses the contents in a power failure. Those controller cards that are known to be better than others, are with battery-backup units that mean the card possesses a battery maintaining the power to the cache in case of loss of system power. Power can be restored on the data and it will be recorded on the disk drives.

Generally almost most of the disk drives have caches and a few of them are write-through. Ahomework helpcan show that some are write-back, and the same concerns about data loss exist for write-back drive caches as for disk controller caches. Consumer-grade IDE and SATA drives are chiefly to get write-back caches that will not endure a power failure. There are many solid-state drives that have unstable write-back caches.

Such kind of caches can classically be disabled and the method varies depending on operating system and drive type:

On Linux, IDE drives can be queried using hdparm -I; write caching is enabled if there is a * next to Write cache. hdparm -W can be used to turn off write caching. SCSI drives can be queried using sdparm. Use sdparm --get=WCE to check whether the write cache is enabled and sdparm --clear=WCE to disable it.

On FreeBSD, IDE drives can be queried using atacontrol and write caching turned off using hw.ata.wc=0 in /boot/loader.conf; SCSI drives use sdparm.

On Solaris, the disk write cache is controlled by format -e. (The Solaris ZFS file system is safe with disk write-cache enabled because it issues its own disk cache flush commands.)

On Windows, if wal_sync_method is open_datasync (the default), write caching can be disabled by unchecking My Computer\Open\disk drive\Properties\Hardware\Properties\Policies\Enable write caching on the disk. Alternatively, set wal_sync_method to fsync or fsync_writethrough, which prevent write caching.

On Mac OS X, write caching can be prevented by setting wal_sync_method to fsync_writethrough.

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